Increasing the optical path is an alternative to improve sen-sitivity in spectrophotometry [30–33].
This can be successfully performed with liquid-core waveguide cells, which are built with materials with refractive indexes lower than the liquid inside it.
Amorphous fluoropolymers from the Teflon AF® family have been used to this aim, resulting in sensitivity up to 500-fold higher that the achieved with usual 1-cm cells [30,32].
Long pathlength spec-trophotometry was recently applied for cyanide determination in exhaled breath, human saliva and fruit seeds based on reaction with cobinamide [16,17], achieving detection limits at the nanomolar range.